1. Field of the Invention
This invention relates generally to a device for use in the assembly and disassembly of valves and more particularly to a device for compressing the springs in the valve seat of a top entry ball valve during assembly and disassembly.
2. Description of the Prior Art
Top entry ball valves have been a standard type of valve for many years. The valve includes two aligned flow ports with a ball placed between the ports. The ball contains a passage which may be turned so as to be aligned with the flow ports and permit the flow of the controlled fluid. Valve seats are placed between the ball and each port to seal the assembly. Recent valves have included spring loaded seats so as to effect a more perfect seal. While this aids the operation of the valve, it makes the assembly and disassembly of the device more complex. Generally, in order to remove the ball it is first necessary to move the seats backwardly against the force of the springs. The prior art shows many methods for performing this operation.
U.S. Pat. No. 4,266,566 to Kacal and Partridge shows a top entry ball valve having a spring loaded valve seat. In order to retract the seats, the ball carries a front cam face which engages the seat when the valve is fully opened. This retracts the seat, which may be locked in this position by means of a pin. The pin screws into the housing and holds the spring by frictional contact. This device requires that additional equipment be added to both the ball and housing, making the device more expensive and more subject to failure. In situations where the seats contain deposited solids which make the retraction difficult, it is necessary to apply considerable force through the ball and actuator assembly, risking damage to these parts.
Another method utilized for holding the seat in engagement with the ball is the use of an advancing screw having a pointed end. Instead of using a spring to apply the force to the valve seat, a screw is advanced forcing the seat toward the ball. Examples of this arrangement are seen in U.S. Pat. Nos. 3,171,431 and 3,037,738. These devices have the disadvantages of requiring adjustment of the screw and the resultant lack of precision. In addition, there is no mechanism for forcing the valve seat backwardly after the advancing force is removed. In cases of valves with deposited solids, the retraction of the seat may be difficult.
A third method for retraction of a valve seat is seen in U.S. Pat. No. 3,985,334. The valve includes an eccentric mounted on a shaft which is in engagement with the seat. When the shaft is rotated the eccentric forces the seat backwardly. This device requires the inclusion of additional moving parts and hence additional uncertainty in its operation. Limited amounts of force can be applied when deposited solids are present hence this mechanism may not always be effective.